ecu's are the same. the auto tranny Maximas have a seperate tranny computer that is bolted right above the engine ecu. Some things that might cause a problem are the IACV, if the VE engine has it. I'm a VG guy and if you swap the trannies it's also a good idea to swap the idle air control valve (IACV) because on an auto there is more drag from the tranny and therefore needs more air at idle to keep it idling correctly. You will have to drill some holes in the fire wall for the clutch master cylinder to bolt to and you will also need to get a clutch pedal and mount it. You may also want to get a brake pedal from a manual tranny maxima. There's quite a bit more and BlueBOB is right, you might try searching the org for more info. You
will notice an increase in performance, contrary to what Ruben said. Manual trannies have a better gear ratio that auto's and stock vs. stock the manual is much quicker. A good idea would be to find a manual tranny with the limited slip differential. The tranny code is RS5F50
V for the limited slip. The open differential tranny has the code RS5F50A. Good luck.
This may help. It's for a 4th gen but will give you a general idea
http://www.hlh0501.com/5spdconversion.htm